Why Too Much Vitamin D Can Be Harmful

Much of the news about vitamin D revolves around making sure people get enough of the sunshine vitamin and warning everyone about the health hazards of being vitamin D deficient. But it also turns out that taking too much vitamin D can be harmful, and a new study from Copenhagen explains why.

Too much vitamin D can be dangerous

There's no shortage of studies concerning the benefits of vitamin D and the health risks associated with having low or deficient levels of the nutrient in your blood stream. Low levels of vitamin D have been associated with a wide range of health problems, including depression, severe asthma in children, and Parkinson's disease.

Perhaps the most commonly recognized benefit of vitamin D is its role in making sure calcium reaches the bones to support and maintain bone health, while a vitamin D deficiency is associated with osteoporosis and higher risk of fractures. In fact, research also suggests that higher than normal levels of vitamin D are necessary to ensure the effectiveness of bisphosphonates, which are drugs taken to boost bone density.

On the other hand, some previous studies have suggested that taking high amounts of vitamin D may be harmful. This new large study from the University of Copenhagen highlights the dangers of taking too much vitamin D.

How much vitamin D is too much?
The study involved an evaluation of 247,574 blood samples from the Copenhagen General Practitioners Laboratory, part of Denmark's civil registration system. When the investigators correlated vitamin D levels with mortality, they discovered the following:

The vitamin D level associated with the lowest death rate was 50 nanomoles per liter (nmol/L)

The death rate among people who had a vitamin D level of less than 10 nmol/L was 2.31 times higher than among individuals with a vitamin D level of 50 nmol/L

The death rate among individuals with a vitamin D level of more than 140 nmol/L was 1.42 higher than those at the 50 nmol/L level

At this point, scientists cannot explain why high levels of vitamin D are associated with a greater death rate. One of the study's authors, Darshana Durup, a PhD student, explained that "We hope that our study will inspire others to study the cause of high mortality with a high level of vitamin D."

Advertisement

Previous studies of vitamin D
The findings of several previous studies have indicated that high levels of vitamin D may be harmful. A recent Johns Hopkins study, for example, indicated that high vitamin D levels were associated with blood vessel inflammation, which is a risk for heart disease.

An Archives of Dermatology study reported that high normal levels of vitamin D have been associated with an increased risk of nonmelanoma skin cancer.

One study, however, suggested that a single megadose of vitamin D could be beneficial for women who experience severe menstrual cramps. In that study, one 300,000 IU dose five days before women began their menstrual cycle was effective in reducing the severity of menstrual cramping.

It appears clear there is a great need for more research into the risks and benefits of various levels of vitamin D. As for the current study, which is the largest one of its kind, the findings suggest too much vitamin D is associated with a higher risk of death.

The 50 nmol/L is how vitamin D is measured in the blood when you get a blood test to determine your vitamin D status, so this is definitely a useful figure. A vitamin D blood test does not give you a dosage--the dosage, which for vitamin D is in International Units (IUs) would be determined by your doctor so you could then bring your blood levels of vitamin D up to a healthy range, and the range is measured in nmol/L.